Shelf Sea Biogeochemistry blog

Monday, 24 November 2014

The importance of zooplankton poo

Ocean research cruise blog of Jonathan Sharples

At dawn this morning we reached the end of the iron sampling
transect, crossing onto the edge of the continental shelf at a depth of
about 250 metres. Quite a stunning sunrise, with flat calm seas. Not
what you’d expect for November. The dreadful-looking forecast for the
end of the week also appears to have dissipated, so we might be able to
push our work further north into the Celtic Sea.

end of iron transect

We are about to head southeast for an hour or so, to return to the
shelf edge site that we spent 3 days on earlier in the cruise. We need
to repeat some of the Snowcatcher work there, and also the zooplankton
biologists on board want to find some more salps and jellyfish to try
out some experiments to determine how much they are eating and also what
happens to the waste material that they excrete. I’ve asked the
children at Churchtown Primary School in Southport to have a think about
this problem – how quickly does a salp waste pellet (i.e. a salp poo)
sink through the sea? It’s an important thing for us to know about. A
fast sinking particle doesn’t give the bacteria in the water much time
to breakdown the organic material before the pellet reaches the seabed. A
slow-sinking pellet can be broken down into inorganic material before
it reaches the seabed, and that inorganic material is then returned to
the water where it is accessible to the phytoplankton. Also, sinking
quickly means that the carbon in the pellet is removed from the ocean
surface (and the atmosphere) very quickly – you could argue that the
stability of Earth’s climate owes a great deal to zooplankton poo.